1. Field of the Invention
This invention relates to a hologram, more particularly, a volume phase hologram, and a process for producing the hologram.
2. Description of the Prior Art
Holography is a technique that a coherent wave such as laser is projected to a body and the amplitude and phase are modulated depending on the shape of the body, the coherent wave reflected or passing through is recorded (this is hologram), and the hologram is irradiated again with laser to form an optical image of the original body.
Heretofore, there have been studied and developed various hologramic recording materials.
For example, there are now provided bleach-out silver salts (U.S. Pat. No. 3,672,744), photoresist, thermoplastics, gelatine dichromate (U.S. Pat. No. 3,617,274), inorganic glass materials, and ferroelectric substances.
Hologramic recording materials should have, in general, the following characteristics:
(1) High sensitivity to laser, in particular, in a visible wavelength region; PA1 (2) High resolution; PA1 (3) High diffraction efficiency of the resulting hologram; PA1 (4) Less noise of the resulting hologram; PA1 (5) The resulting hologram is stable; and PA1 (6) Easy recording and regeneration. PA1 (i) exposing to an interference pattern of laser a film-like sensitive member for recording holograms which is mainly composed of a polymer selected from the group consisting of polyvinylcarbazole, alkyl-substituted derivatives thereof and halogen-substituted derivatives thereof and is sensitized to a radiation by using an iodine compound, PA1 (ii) swelling the sensitive member in a first solvent until a volume of the sensitive member becomes 120% or more based on the volume immediately after the exposure and simultaneously eluting most of the iodine compound, and PA1 (iii) transferring the sensitive member into a second solvent to treat the sensitive member until the volume of the sensitive member becomes 110% or less based on the volume immediately after the exposure. PA1 (i) Exposing to an interference pattern of laser a film-like sensitive member for recording holograms which is mainly composed of a polymer selected from the group consisting of polyvinylcarbazole, alkyl-substituted derivatives thereof and halogen-substituted derivatives thereof and is sensitized to a radiation by using an iodine compound, PA1 (ii) soaking the sensitive member in a first solvent to elute and remove most of the iodine compound without eluting the polymer, PA1 (iii) then swelling the sensitive member in a second solvent until a volume of the sensitive member becomes 120% or more based on the volume immediately after the exposure, and PA1 (iv) transferring the sensitive member into a third solvent to treat the sensitive member until the volume of the sensitive member becomes 110% or less based on the volume immediately after the exposure.
None of prior art materials have all the above mentioned characteristics. Only a few prior art materials have some of those characteristics.
Among prior art materials, bleach-out silver salts and dichromated gelatine are practically used, but the former requires a bleach-out treatment in addition to usual treatments and the resulting holograms are of poor lightfastness, and the latter gives a hologram of poor humidity resistance and poor shelf stability.